1. Field of the Invention
The present invention relates to a pigment dispersion which is characterized by comprising surface-modified carbon black with an aminosilane compound and a polycarboxylic acid-based water-reducing agent, and a black water-reducing agent using the same.
2. Description of the Related Art
A water-reducing agent is a mixing agent for improving workability of concrete as a main purpose, which can reduce the amount of concrete to be used and improve strength thereof, leading to a saving in cement. The water-reducing agents for cement can be divided broadly into three groups of lignin-based, naphthalene-based and polycarboxylic acid-based water-reducing agents. They exhibit good flowability and durability in the order as listed above. The goal of such a water-reducing agent is fundamentally to improve water-reducing capability of cement.
Recently, it has been demonstrated that the use of a naphthalene-based water-reducing agent as a dispersing agent for carbon black is effective in reducing water-cement ratio. However, since the naphthalene-based water-reducing agent has a disadvantage of having lower water-reducing capability than the polycarboxylic acid-based water-reducing agent, there is a limitation to exhibit high performance.
U.S. Patent Application Publication No. 2004-0231567 discloses a method of suspending iron oxide and carbon black by using a polycarboxylic acid-based dispersing agent. However, according to this method, pigments are introduced only into certain specific dispersing agents synthesized through a complicated polymer synthesis process, and thus, there is a problem in that it is impractical.
Therefore, there is a need to develop a method for using the conventional polycarboxylic acid-based water-reducing agents as a dispersing agent for carbon black.
The present inventors have endeavored to develop a method of using the conventional polycarboxylic acid-based water-reducing agent with good performance as a pigment dispersing agent for carbon black, and therefore, found that when the surface of carbon black is modified with an aminosilane compound so as to introduce functional groups, and a pigment dispersion is manufactured by using thus obtained surface-modified carbon black together with a polycarboxylic acid-based water-reducing agent, it is possible to manufacture ultra-high-strength concrete with good dispersability and displaying black color of the water-reducing agent and cement at the same time.